Τομέας Πυρηνικής Φυσικής και Φυσικής Στοιχειωδών Σωματιδίων
Library of the School of Science

2016-02-19

2016

Τσιριντάνης Νικόλαος

Χριστίνα Κουρκουμέλη Καθηγήτρια (επιβλέπουσα), Δημήτρης Φασουλιώτης, Θεόδωρος Αλεξόπουλος

Search for new heavy, charged gauge bosons with the ATLAS detector

English

Αναζήτηση νέων βαρέων φορτισμένων διανυσματικών μποζονίων με τον ανιχνευτή ATLAS

The subject of this thesis is the search for new heavy charged bosons beyond
the predictions of the Standard Model. The existence of new heavy charged
vector bosons is investigated in events containing a muon and neutrino pair.
Neutrinos are observed indirectly via the presence of high missing transverse
energy. We analyze data from proton-proton collisions at center of mass energy
of 8 TeV, collected by the ATLAS detector during the operation of the Large
Hadron Collider in the years 2011-2012, corresponding to an overall luminosity
of
20.3 fb-1.
Two main new-physics scenarios are investigated: The first new-physics scenario
that is considered in this thesis is the Sequential Standard Model (SSM). This
model proposes the existence of additional heavy gauge bosons, of which the
charged ones are commonly denoted as W. The W has the same couplings to
fermions as the Standard Model W boson and a width that increases linearly with
the W mass.
The second new-physics scenario that is considered proposes the existence of
charged partners, denoted
W*, an excited state of the Standard Model W boson. The anomalous
(magnetic-moment type) coupling of the W* leads to kinematic distributions
significantly different from those of the W.
Α strict data event selection is applied in order to reduce the background,
which comes mainly from W boson decays. All background sources were simulated,
except the multijet background, which was estimated from the experimental data.
Finally,all sources of systematic uncertainty are carefully evaluated.
The analysis of data showed that the number of events observed is consistent
with the number of background events expected, so there is no evidence for the
existence of new, heavy charged gauge bosons. Therefore, limits are set to the
σ * B (cross-section * branching ratio) for W' and W* in the mass range of 0.5
- 4 TeV.
In the analysis presented in this thesis, the limits are considerably improved
in the region covered by the previous search.

New heavy gauge bosons, Muon, Missing transverse energy, proton proton collisions, LHC, ATLAS

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Yes

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